Liquid level indicating and warning devices are well known and have been in use for many years to indicate the levels of oil, water and the like in storage tanks. For example, a U.S. patent of McGill (U.S. Pat. No. 3,545,272) discloses a liquid level warning device including a hollow buoyant member having a pair of electrical contacts at one end thereof and a ball of mercury or other moveable current carrying material mounted therein. The buoyant member is connected to a flexible carrier line which extends downwardly to a weight and then upwardly through an opening within the tank. The electrical contacts are connected to a source of electricity. Then, the distance between a buoyant member and the weight is adjustable so that normally when the tank is substantially filled the buoyant member will be disposed along a vertical axis and when the liquid falls to a pre-determined level the buoyant member will be disposed at a slight downward angle relatively to the horizontal plane so that the ball will roll by gravity into engagement with the electrical contacts to complete a circuit to an alarm or other indicator.
A more recent patent of Nelson (U.S. Pat. No. 5,283,569 discloses a float activated flood warning system with remote telephone reporting. The Nelson patent shows a flood warning system including a stilling well having three spaced apart switches therein for detecting the level of flood waters. Upon the water level reaching and closing a float switch a flood warning message is sent to a remote location.
Float switches for use in liquid level indicating and alarm systems are also well known. For example, a U.S. Pat. No. 5,824,980 discloses a float switch having a closed hollow body and a suspending and tethering electrical cable connected to the hollow body for conducing electrical power to and from a micro-switch confined within the body. A switch actuator is engaged and disengaged by a weight within the body. This weight actuator is pivotably supported within the hollow body and has a center of gravity which is offset from a central longitudinal axis of the sensor.
Notwithstanding the above, it is presently believed that there is a need and a potential commercial market for a liquid level indicator and alarm in accordance with the present invention. There should be a commercial market because such systems are compact, economical and work with a battery and more specifically a nine volt battery. Further, the use of the battery is minimized by the use of LEDs and by a push button switch so that the LEDs are only energized when the switch is held in an open position.
Further, a unique float switch in accordance with the present invention eliminates the need for mercury and at the same time provides a durable and reliable unit. A further advantage resides in an override for sounding an alarm even though the visual indicator is turned off as well as a master switch which turns off the alarm as well as the visual indicators. A system in accordance with the present invention provides a visual signal to show the status of the tank i.e. full, three-quarters full, half-full, one-quarter full etc. and provides that signal only upon pushing a push button switch. Further, the system includes an alarm that is independent of the visual signals but may be turned off by a master switch.
It is also believed that the liquid level indicator and alarm in accordance with the present invention can be manufactured at a relatively low cost and sold at a competitive price. In addition, such devices can be easily installed, easy to repair or replace, accurate and flexible in that adjustments can be made to sound an alarm at various levels. For example, the system could be readily modified to sound an alarm at a first selective level as for example when the tank reaches the one-quarter level and at a continuous and perhaps louder alarm when there is only one-tenth or less of the tank capacity remaining.